This continuation of a previously initiated project seeks to assess the frequency and occurrence of drug dependence syndromes in the non-institutionalized population of the United States, age 15-54 years old, and to test hypotheses about suspected prevalence correlates and risk factors for drug dependence. As such, the project complements and strengthens information on psychoactive drug use that can be derived from the National Household Survey on Drug Abuse. The first part of this project has involved statistical analyses of the survey data in order to estimate prevalence of drug dependence (by drug type), and the proportion of drug users who had become drug dependent (also by drug type). The data for these analyses derived from confidential interviews with 8,098 survey respondents, who had been selected by probability sampling to serve as a nationally representative sample of 15-54 year old Americans, and who then were recruited for the survey's diagnostic assessments. These analyses were extended to include tests of hypotheses about correlates of prevalence of drug dependence in the U.S. population, which have provided clues about suspected risk factors. As a result of this work, for the first time we have national estimates for the prevalence of drug dependence syndromes, and we have been able to make comparisons across specific drug types, based on data from a nationally representative sample. The results also have provided important confirmation of some previous findings about sociodemographic correlates of drug dependence. For example, African-Americans were no more likely than White Americans to have become drug dependent, with or without statistical adjustment for socioeconomic differences between these population sub-groups. Further, against a backdrop of generally higher prevalence values for men versus women, it was important to note higher female prevalence of dependence on sedative-hypnotic-anxiolytic drugs among women of middle age. In the past year's extension of this project, we have investigated these cohort differences in prevalence of drug dependence in more detail; we are testing hypotheses about the age of onset of drug use and the risk of later drug problems; and we are attempting to understand the natural history or clinical course of treated and untreated drug dependence in relation to characteristics such as education and occupation. In addition to the 1994 paper on this project, a new paper based on the 1994-95 work already has been produced, and recently has been published in the Archives of General Psychiatry (1995).